Field of the Invention
The present invention relates to an additional fuel tank, particularly to a bladder-free fuel tank for aircraft applications in which the net volume to be occupied by fuel is maximized and mechanical stiffness of the bladder-free fuel tank is enhanced.
Description of the Background Art
U.S. Pat. No. 7,093,470 B2 is related to methods of making integrally stiffened axial load carrying skin panels for primary aircraft structure and fuel tank structures. According to U.S. Pat. No. 7,093,470 B2, a method of making a skin panel is disclosed according to which a starting plate is machined to a final part geometry including a skin and at least one integral stiffener machined into the plate and extending generally outwardly from the skin. Further, an explosive forming of the machined plate is performed with its integral stiffener against a forming surface of a rigid dye having a contour which at least substantially is in accordance with the desired curvature for the skin panel, the explosive forming causing the machined plate to substantially conform to the contour of the forming surface to at least one of an uniaxial curvature and a biaxial curvature. Stiffening features are ribs, stiffeners, stringers, frames outer chords and the like.
WO 2007 121969 A1 is related to an inner container surrounded by an outer container used for receiving a cryogenic liquid. Disclosed is a flat inner container, especially an internal tank for a road vehicle which is surrounded by an outer container and is used for receiving a cryogenic liquid, particularly fuel. The inner container is characterized by a combination of the following features: A longitudinally extending monolithic base with a top wall and a bottom wall, which are connected to also longitudinally extending sidewalls and with at least two longitudinally extending, substantially straight webs that connect the bottom wall to the top wall so as to form at least one longitudinally extending chamber. The chamber is arranged between the webs extending along the entire length of the base as well as from the bottom wall to the top wall and has a predetermined width between the webs. At least two caps tightly seal the two open ends of the base at the periphery. The top wall and/or the bottom wall is/are provided with an arch relative to a planar reference top wall and/or reference bottom wall, the distance of the arch between the inner contour of the top wall and/or the bottom wall and the planar reference top wall and/or bottom wall amounting to less than 30% of the width of the chamber in the center between the webs.
US 2012/0181288 A1 is related to a tank having integral restraining elements and an associated fabrication method. According to US 2012/0181288 A1 a tank and an association fabrication method are disclosed which may limit the damage otherwise occasioned by the impact of a ballistic projectile. The tank may include a wall assembly defined between outer and inner walls and a plurality of restraining elements that extend between the walls. The restraining elements may be formed to have a plurality of layers of material that form not only the restraining element but also portions of the inner and/or outer walls. For example, the tank may include a plurality of cells positioned adjacent to one another with each cell forming portions of two adjacent restraining elements and portions of the inner and/or outer walls. A corresponding method for fabricating a tank including a wall assembly having a plurality of restraining elements is also provided.
U.S. Pat. No. 7,090,167 B2 is related to a method and apparatus for liquid containment such as for aircraft fuel vessels. A vessel can include a first surface portion, a second surface portion spaced apart from the first surface portion and a core positioned between the first and second surface portions. The core can be sealably connected to the first and second surface portions and can be positioned to carry a load from at least of the first and second surface portions to the other. The core can include a plurality of cells separated by cell walls, at least some of which have wall openings positioned to provide liquid communication between adjacent cells.
U.S. Pat. No. 8,550,403 B2 is related to an aircraft fuel tank. An aircraft fuel tank is capable of suppressing electrostatic charging of for example by flow electrification with the fuel. The aircraft fuel tank comprises an upper skin and a lower skin that exhibit conductivity and form a portion of a container for storing fuel, an internal structure formed from metal and an inner surface layer which has semiconductor properties or insulating properties and is formed in an integral manner on the inner surfaces of the upper skin and the lower skin in the location where the internal structure contacts the upper skin and the lower skin, as well as in the surrounding portion thereof, wherein the inner surface layer is formed at least in the surround portion from a material having semiconductor properties.
EP 2 048 079 A2 is related to a fuel tank assembly in an associated method. A fuel tank assembly and associated method are provided which may limit the damage otherwise occasioned by the impact of a ballistic projectile. The fuel tank assembly may include a bladder defined between interior and exterior bladder walls, with the interior bladder wall defining a volume for storing fuel. The exterior bladder wall is at least as more rigid than the interior bladder wall. The fuel tank assembly can also include connectors between the exterior and interior bladder walls to at least partially limit the expansion of the bladder. The fuel tank also includes an inlet opening to the bladder to permit a pressurized gas to be introduced into the bladder. The fuel tank assembly may also include a valve through the interior bladder wall into the volume for storing fuel to permit at least some of the pressurized gas to be introduced therein.
U.S. Pat. No. 5,320,247 is related to storage tanks with internal support ribs. A method of forming a storage tank from an existing matrix tank comprises adding spaced internal support ribs. The interior surface of the matrix tank is covered with a layer of fibrous reinforced resinous material to form a main body and internal support ribs are added. The main body and support ribs are secured together such that the ribs protrude inwardly. The formed tank is fully and independently capable of containing liquid and withstanding normal internal and external load forces. A double walled formed storage tank system is also provided wherein an inner wall between or on the internal support ribs is added.
Fuel tanks and/or additional fuel tanks such as additional center tanks for aircraft applications having bladders integrated therein are manufactured very costly and constitute a compromise in view of the factors weight, production and maintenance costs and in view of integration of in-fuel-tank equipment. Further, the use of a bladder in a fuel tank comes along with a loss of usable tank volume. Known honeycomb-structured tanks suffer the drawback of being applicable only subject to specific design, production and maintenance know-how to create an additional fuel tank or a fuel tank for an aircraft application with acceptable costs and economical risk.